Swimming physiology of European silver eels (<Emphasis Type="Italic">Anguilla anguilla</Emphasis> L.): energetic costs and effects on sexual maturation and reproduction |
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Authors: | Email author" target="_blank">Arjan?P?PalstraEmail author Guido?E?E?J?M?van?den Thillart |
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Institution: | (1) Molecular Cell Biology, Institute of Biology, Leiden University (IBL), Leiden, 2333 CC, The Netherlands;(2) Present address: Departament de Fisiologia, Facultat de Biologia, Universitat de Barcelona, 08028 Barcelona, Spain |
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Abstract: | The European eel migrates 5,000–6,000 km to the Sargasso Sea to reproduce. Because they venture into the ocean in a pre-pubertal
state and reproduce after swimming for months, a strong interaction between swimming and sexual maturation is expected. Many
swimming trials have been performed in 22 swim tunnels to elucidate their performance and the impact on maturation. European
eels are able to swim long distances at a cost of 10–12 mg fat/km which is 4–6 times more efficient than salmonids. The total
energy costs of reproduction correspond to 67% of the fat stores. During long distance swimming, the body composition stays
the same showing that energy consumption calculations cannot be based on fat alone but need to be compensated for protein
oxidation. The optimal swimming speed is 0.61–0.67 m s−1, which is ~60% higher than the generally assumed cruise speed of 0.4 m s−1 and implies that female eels may reach the Sargasso Sea within 3.5 months instead of the assumed 6 months. Swimming trials
showed lipid deposition and oocyte growth, which are the first steps of sexual maturation. To investigate effects of oceanic
migration on maturation, we simulated group-wise migration in a large swim-gutter with seawater. These trials showed suppressed
gonadotropin expression and vitellogenesis in females, while in contrast continued sexual maturation was observed in silver
males. The induction of lipid deposition in the oocytes and the inhibition of vitellogenesis by swimming in females suggest
a natural sequence of events quite different from artificial maturation protocols. |
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